Power line coupling device and method

ABSTRACT

A power line coupler for communicating data signals over a power distribution system having a first and second overhead energized medium voltage power line conductors is provided. In one embodiment, the coupler includes a first lightening arrestor having a first end and a second end, wherein the first end of the first arrestor is connected to the first power line conductor. The coupler further includes a first high frequency impedance having a first end connected to the second end of the first lightening arrestor and the first impedance having a second end connected to a neutral conductor of the power line distribution system. The coupler may further include a second lightening arrestor having a first end and a second end, wherein the first end of the second arrestor is connected to the second power line conductor. The coupler further including a second high frequency impedance having a first end connected to the second end of the second lightening arrestor and a second end connected to the neutral conductor. The first high frequency impedance and the second high frequency impedance may each comprise an air core coil that forms an inductor. The coupler may further include a balun having a first winding and a second winding, wherein the first winding is coupled to a communication device, and wherein the second winding has a first end connected to the first end of the first high frequency impedance and a second end connected to the first end of the second high frequency impedance.

FIELD OF THE INVENTION

The present invention generally relates to power line communicationdevices and methods, and more particularly to a device and method forcoupling a broadband power line communication device to an overheadmedium voltage power line.

BACKGROUND OF THE INVENTION

The need for reliable broadband communication networks to deliver dataservices such as voice over internet protocol (VoIP), video, internetweb data, email, file sharing, stereo over IP, and other such servicesis increasing. In response to these demands, the communicationinfrastructure is expanding to include many types of communicationnetworks beyond the public switched telephone network. A power linecommunication system (PLCS) is an example of a communication network inthe expanding communication infrastructure.

A PLCS uses portions of the power system infrastructure to create acommunication network. In addition to carrying power signals, existingpower lines that run to and through many homes, buildings and offices,may carry data signals. These data signals are communicated on and offthe power lines at various points, such as, for example, in or nearhomes, offices, Internet service providers, and the like.

There are many challenges to overcome when using power lines for datacommunication. For example, devices that communicate over power lines,such as medium voltage power lines, need a method of coupling datasignals to and from the medium voltage power line. Medium voltage powerlines can operate from about 1000 V to about 100 kV, and often carryhigh amperage. Consequently, coupling to a medium voltage power linegives rise to safety concerns for the user installing the couplingdevice.

The coupling device should be designed to provide safe and reliablecommunication of data signals with a medium voltage power line—carryingboth low and high current—in all outdoor environments such as extremeheat, cold, humidity, rain, wind, high shock, and high vibration. Also,because many power line communication devices are connected to a lowvoltage power (and its associated coupler), the coupler must be designedto prevent that dangerous MV voltage levels from being provided to thecustomer premises on the low voltage power line. In addition, a couplingdevice should be designed so that it does not significantly compromisethe signal-to-noise ratio or data transfer rate and facilitatesbi-directional communication. In addition, the coupling device (orcoupler as referred to herein) should enable the transmission andreception of broadband radio frequency (RF) signals used for datatransmission in MV cables.

Finally, because a coupler may used throughout a PLCS, it must beeconomical to manufacture and easy to install by power line personnel.Various embodiments of the coupler of the present invention may providemany of the above features and overcome the disadvantages of the priorart.

SUMMARY OF THE INVENTION

The present invention provides a power line coupler for communicatingdata signals over a power distribution system having a first and secondoverhead energized medium voltage power line conductors. In oneembodiment, the coupler includes a first lightening arrestor having afirst end and a second end, wherein the first end of the first arrestoris connected to the first power line conductor. The coupler furtherincludes a first high frequency impedance having a first end connectedto the second end of the first lightening arrestor and the firstimpedance having a second end connected to a neutral conductor of thepower line distribution system. The coupler may further include a secondlightening arrestor having a first end and a second end, wherein thefirst end of the second arrestor is connected to the second power lineconductor. The coupler further including a second high frequencyimpedance having a first end connected to the second end of the secondlightening arrestor and a second end connected to the neutral conductor.The first high frequency impedance and the second high frequencyimpedance may each comprise an air core coil that forms an inductor. Thecoupler may further include a balun having a first winding and a secondwinding, wherein the first winding is coupled to a communication device,and wherein the second winding has a first end connected to the firstend of the first high frequency impedance and a second end connected tothe first end of the second high frequency impedance.

The invention will be better understood by reference to the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described in the detailed description thatfollows, by reference to the noted drawings by way of non-limitingillustrative embodiments of the invention, in which like referencenumerals represent similar parts throughout the drawings. As should beunderstood, however, the invention is not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1 is a block diagram of an example power line communication system;

FIG. 2 is a schematic diagram of a coupling device according to anexample embodiment of the present invention;

FIG. 3 a is a schematic diagram of a coupling device according toanother example embodiment of the present invention;

FIG. 3 b is a schematic diagram of a coupling device according to yetanother example embodiment of the present invention;

FIG. 4 is a schematic diagram depicting principles of phase differentialcommunication practiced by some example embodiments of the presentinvention;

FIG. 5 is another schematic diagram depicting principles of phasedifferential communication practiced by some example embodiments of thepresent invention;

FIG. 6 is a schematic diagram of a coupling device according to anotherexample embodiment of the present invention;

FIG. 7 illustrates an example implementation of a coupling deviceaccording to an example embodiment of the present invention; and

FIG. 8 illustrates an example configuration of two air core inductorsand a balun according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as particular networks,communication systems, computers, terminals, devices, components,techniques, data and network protocols, power line communication systems(PLCS), software products and systems, enterprise applications,operating systems, development interfaces, hardware, etc. in order toprovide a thorough understanding of the present invention.

However, it will be apparent to one skilled in the art that the presentinvention may be practiced in other embodiments that depart from thesespecific details. Detailed descriptions of well-known networks,communication systems, computers, terminals, devices, PLCSs, components,techniques, data and network protocols, software products and systems,operating systems, development interfaces, and hardware are omitted soas not to obscure the description of the present invention.

System Architecture and Power Line Communication System

FIG. 1 shows an example embodiment of a portion of a power linecommunication system (PLCS) 104. The PLCS 104 implements a communicationnetwork or sub-network using portions of the power system infrastructure101 and various power line communication devices (PLCD) 138, 139, 135.The PLCD 138, 139, 135 may be coupled to power lines 110, 114 of thepower system infrastructure 101 to transmit and receive communications.

The power distribution system infrastructure 101 includes power lines,transformers and other devices for power generation, power transmission,and power delivery. A power source generates power, which is transmittedalong high voltage (HV) power lines for long distances. Typical voltagesfound on HV transmission lines range from 69 kilovolts (kV) to in excessof 800 kV. The power signals are stepped down to medium voltage (MV)power signals at regional substation transformers. MV power lines 110carry power signals through neighborhoods and populated areas. Typicalvoltages found on MV power lines 110 power range from about 1000 V toabout 100 kV. The power signals are stepped down further to low voltage(LV) levels at distribution transformers. LV power lines 114 typicallycarry power signals having voltages ranging from about 100 V to about600 V. A distribution transformer may function to distribute one, two,three, or more phase voltages to the customer premises, depending uponthe demands of the user. In the United States, for example, these localdistribution transformers typically feed anywhere from one to ten homes,depending upon the concentration of the customer premises in aparticular area. Distribution transformers may be pole-top transformerslocated on a utility pole, pad-mounted transformers located on theground, or transformers located under ground level.

The PLCS 104 may provide user services, such as high speed broadbandinternet access, mobile telephone communications, broadbandcommunications, streaming video and audio services, and othercommunication services to homes, buildings and other structures such asto each room, office, apartment, or other unit of multi-unit structures.Communication services also may be provided to mobile and stationarydevices in outdoor areas such as customer premises yards, parks,stadiums, and also to public and semi-public indoor areas such as subwaytrains, subway stations, train stations, airports, restaurants, publicand private automobiles, bodies of water (e.g., rivers, bays, inlets,etc.), building lobbies, elevators, etc.

In various configurations the PLCS 104 may include one or more powerline communication networks, such as an overhead power linecommunication network and/or an underground power line communicationnetwork. The PLCS 104 may include a plurality of communication nodes 128which form communication links using power lines 110, 114 and othercommunication media. Various user devices 130 and power linecommunication devices (PLCD) 138, 139, 135 may transmit and receive dataover the links (including power line links, wireless links, fiber opticlinks, etc.) to communicate via an IP network 126 (e.g., the Internet).Among the data may be user data, control data, and/or power distributionparameter data. A communication node 128 may comprise a backhaul node132, an access node 134, or a repeater node 135. A given node 128 mayserve as a backhaul node 132, access node 134, and/or repeater node 135.The various nodes may include respective power line communicationdevices. A PLCD may be coupled to an MV power line 110 and/or an LVpower line 114.

PLCD Coupler 202:

FIG. 2 shows a portion of a PLCS in which a power line communicationdevice (PLCD) 202 is coupled to a single phase conductor 110 (which mayform part of an overhead three-phase medium voltage (MV) power line) viaa coupling device 204, according to an example embodiment of the presentinvention. The PLCD 202 illustrated in FIG. 2, and in the subsequentfigures, may be any of the PLCD 138, 139, 135 described herein, and mayinclude a modem or other transceiver device 203. The coupling device 204may couple the PLCD 202 to the power line 110 at any point along thepower line 110. In some embodiments the coupling may occur in thevicinity of a distribution transformer 112.

This example embodiment includes a lightening arrestor 216 (also knownas a surge arrestor) coupled on its first side to the MV power linephase conductor 110 and on its second side to a first end of an air coreinductor 214 via a conductor 226 (e.g., a length of wire) at node 219.The second end of the air core inductor 214 is connected to the neutralconductor 210 (which typically runs pole to pole in parallel with the MVpower line 110) of the power distribution system, and which is alsoconnected to earth ground via a ground conductor 224. The coupler 204may also include a balun 212 having a first winding 220 and a secondwinding 218. Two terminals of the PLCD 202 may be coupled to the twoends of the second winding 218 of the balun 212 via a cable 222. A firstend 220 a of the first winding 220 of the balun 212 may be coupled tothe neutral conductor 210 and the second end of the air core inductor214. The second end 220 b of the first winding 220 of the balun 212 maybe coupled to the second end of the lightening arrestor 216 and thefirst end of the air core inductor 214 at node 219. As depicted, thesecond end 220 b of the first winding 220 is coupled to the lighteningarrestor 216 via a conductor 226 but, alternately may be directlyconnected to the arrestor 216 at node 219 (and to the air core inductor214) without a conductor 226.

In summary, the transceiver 203 of the PLCD 202 may be coupled to bothends of the air core inductor 214 via the cable 222 and the balun 212.In other words, the air core inductor 214 may be connected in parallelwith the first winding 220 of the balun 212. It is worth noting that thelightening arrestor 216 and air core inductor 215 are connected betweenthe energized MV phase conductor 110 and the neutral conductor 210. Suchplacement provides several advantages. Specifically, the data signalsare communicated differentially in that the difference in voltagebetween the two wires (the MV phase conductor 110 and the neutralconductor 210) is used to convey information. The phase conductorcarries the power line communication signal, and the neutral conductorcarries the inverse of the same signal. Thus, distant radiated noisesources tend to add the same amount of noise (called common-mode noise)to both wires, causing the voltage difference between the conductors toremain substantially unchanged due to such noise. Using such signalingmethod, the power line communication system embodiments may have a lowersusceptibility to distant radiated noise than some other systems. Invarious embodiments, this embodiment of the coupler 204 may couple powerline communications to one or more phases of a two phase, three phase orother multi-phase phase power line configuration systems.

The lightening arrestor 216 of the present example and others describedherein provides a capacitance that allows the data signals to passthrough the arrestor 216 while preventing the low frequency (60 Hz) highvoltage power carried by the power line 110 from being conductedtherethrough to the neutral 210. Thus, the lightening arrestor may beconsidered to be a high pass filter. One advantage of using a lighteningarrestor is that they are already mass produced for utilities and,therefore, are relatively inexpensive compared to a custom designedcapacitive device. Another advantage is that utility personnel arealready familiar with installing them. In alternative embodiments, thelightening arrestor 216 of this and the other embodiments describedherein may be replaced with a high voltage capacitor (e.g., a capacitivedevice or a metal oxide varistor device).

The air core inductor 214 provides an impedance to higher frequenciesused to communicate data signals such as between 4 and 50 Megahertz but,(in this embodiment), is designed to allow electricity from a lighteningstrike to the MV power line conductor 110 to pass largely unimpeded. Oneexample embodiment of the air core inductor 214 comprises a fivemicro-Henry air core inductor, which provides an impedance atfrequencies used to communicate data signals, but that has very littleimpedance at frequencies often inherent in a lightening strike (e.g., 10KHz). Hence, the air core inductor 214 may be considered a low passfilter. The impedance of the air core inductor 214 prevents higherfrequency data signals received via the lightening arrestor 216 frombeing conducted directly to earth ground via conductor 224 and, instead,shunts the data signals through the first winding 220 of balun 218 to bereceived via second winding 218 by the modem 203 of PLCD 202. Likewise,when the PLCD 202 is transmitting data signals, the impedance of aircore inductor 214 also prevents the data signals from canceling eachother out at the first and second ends of the first winding 220 andinstead, causes the data signals to be conducted to the MV phaseconductor 110 (via lightening arrestor 216) and the neutral conductor210 from the first winding 220. In other embodiments, instead of an aircore inductor 214 the impedance (i.e., low pass filter) may be providedby other means such as by a ferrite core (or ferrite beads) placedaround a conductor extending between the ends of the first winding 20 ofthe balun 212. However, the air core inductor may have advantages overvarious other means in that it is easy to construct, is light weight,and economical to manufacture. Air core inductor, as used herein, ismeant to refer to an inductor having an inductance that is notsubstantially attributable to a magnetic material. In other words, thecore of the inductor has a permeability approximating one and,therefore, may be formed of air, wood, fiber glass, copper, some typesof steel, a dielectric, or other non-magnetic materials. Use of the aircore inductor reduces the likelihood of saturation.

The air core inductor 214 may be implemented in either a multi-phasesystem or a single phase system. Very low ‘through losses’ may beachieved with the coupler 204 embodiments, which may be controlled bythe balun 212. Specifically, in some embodiments, by increasing theinput impedance of the balun 212 (from the first winding 220) may reducethe through loss (i.e., the reduction in energy) of signals thattraverse the MV phase conductor 110 past the lightening arrestor 216.

One advantage of the coupler 204 is its compatibility with various powerline cables and systems, including for example, 15, 25 and 35 kV cablesand systems. Another advantage of the coupler 204 is that it can beinstalled without interrupting power line service, (i.e., no-outageinstallation).

In an example transmission method, a communication signal is transmittedover the MV power line 110 from PLCD 202. The communication signal istransmitted from the modem 203 of PLCD 202 to the second winding 218 ofbalun 212. The communication signal is induced onto the first winding220. The air core inductor 214 has an impedance that directs the energyof the signal away from the inductor 214, allowing the signal to beapplied differentially to the energized phase conductor 110 (via thelightening arrestor 216) and the neutral conductor 210. Thus, the signalmay be transmitted differentially onto the phase conductor 110 and theneutral conductor 210, and received by another PLCD 202. In addition, insome embodiments the signals also may cross couple from one phaseconductor 110 to another phase conductors 110 (not shown) through air.Thus, the transmitting PLCD 202 may be coupled to one conductor 110,while the receiving PLCD 202 may be coupled to the same conductor 110 orto a different conductor 110. At the receiving PLCD 202, the differencebetween the signals on two of the conductors—the MV phase conductor 110and the neutral conductor—may be detected. Because the PLCD 202 ignoresthe conductors' voltages with respect to ground, small changes in groundpotential from the transmitting PLCD 202 and receiving PLCD 202generally do not affect the receiving PLCD's ability to detect thesignal.

For a received signal, the communication signal may be received at thelightening arrestor, which conducts the high frequency signal to thefirst winding 220 of the balun 212 first, which induces the signal ontothe second winding 218, which is then detected at the PLCD 202. Theinverse of the signal may also be received via the neutral conductor 210and received at the second end 220 a of the first winding 220. Theimpedance of the air core inductor 214 causes the current of the twosignals to flow through the first winding 220 of the balun 212 insteadthrough the inductor 214 to cancel each other out. The use of theinductor 214 in this embodiment (and in the others) allows thelightening arrestor to simultaneously operate as both part of thecoupling device and as a lightening arrestor to afford the utilityinfrastructure (e.g., a transformer) protection (because the air coreinductor 214 will conduct the electricity of a lightening strike). Thedual functionality of some embodiments of the present invention may thusbe well suited for some implementations of power line communicationsystems that include a coupling device at or near each transformer (aspart of a bypass device to bypass data signals around the transformer).

FIG. 3 a shows a portion of a PLCS in which a power line communicationdevice (PLCD) 202 is coupled to a multi-phase medium voltage (MV) powerline 110 via a coupling device 232, according to another exampleembodiment of the present invention. Communications may be transmitteddifferentially over two MV power line phase conductors 110 a, 110 b toand from the PLCD 202. The coupling device 232 may include a balun 234,a pair of air core inductors 214 a,b, and a pair of lightening arrestors216 a,b.

In the embodiment of FIG. 3 a, a first air core inductor 214 a may becoupled to a first lightening arrestor 216 a (via a conductor 226 a)between a first energized conductor 110 a and the neutral conductor 210.Similarly, a second air core inductor 214 b may be coupled to a secondlightening arrestor 216 b (via conductor 226 b) between a secondenergized conductor 110 b and the neutral conductor 210. The balun 234has a first winding 238 and a second winding 236. One end of the firstwinding 238 may be coupled to a first node 219 a to which is connectedto both the first air core inductor 214 a and the first lighteningarrestor's 216 a. Similarly, the second end of the first winding 238 maybe coupled to node 219 b to which is connected both the second air coreinductor 214 b and the second lightening arrestor's 216 b. As previouslydescribed, the lightening arrestors 216 may be replaced with othercapacitive devices (e.g., a high voltage capacitor or a metal oxidevaristor device). The two ends of the second winding 236 may be coupledto two terminals of the PLCD 202, such as via a cable 222. As depictedin FIG. 3 a, conductors 226 a and 226 b, which each may comprise alength of copper wire, may be disposed along side of each other to forma two wire transmission line and thereby improve communications (e.g.,by reducing radiated emissions from the coupler 232).

In the embodiment of FIG. 3 a, the data signals are transmitteddifferentially over two phase conductors of a multi-phase power line(e.g., two phase or three phase). In this embodiment, the air coreinductors 214 a,b again provide an impedance to higher frequencies usedto communicate data signals. Consequently, during transmission the aircore inductors 214 prevent the data signals from being conducted to theneutral conductor and, instead, cause the data signals to be conductedthrough the lightening arrestors 216 a, b onto the two phase conductors110 a,b. For reception, the air core inductors 214 prevent the datasignals from being conducted to the neutral conductor 210, but, instead,cause the data signals to be conducted from the lightening arrestors216, through the balun 234, to the PLCD 202. In addition, the air coreinductors 214 have a very low impedance for frequencies often associatedwith lightening to thereby permit the current from a lightening strikeon one of the MV conductors 110 a,b to be conducted to ground (viaground conductor 214) largely unimpeded.

In another embodiment illustrated in FIG. 3 b, the first air coreinductor 214 a and 214 b are connected to each other on their secondends, and are also connected to the neutral conductor 210 by a commonconductor 317 (instead of via separate conductors as shown in FIG. 3 a).In addition, in this embodiment, the air core inductors 214 may bephysically positioned adjacent the lightening arrestors 216 a,b on autility pole so that the conductors 226 may not be present or, ifpresent, may not form a two pair transmission line.

In some embodiments multiple phase conductors may not be available forimplementing a differential communication method. In such cases or inany case where communication is desired to be implemented on a singleconductor, the communication signal may be injected at two separatelocations along the phase conductor.

FIG. 4 shows a circuit 250 used to illustrate the principles ofdifferential communication for such examples. Data signals (depicted assource Vs) split at point A and traverse along paths B and C towardtransceiver 203 (whose gain equals one for the purposes of thisdescription). The two paths B and C may be the same, except that path Cmay include an additional delay 25 of time duration T1 that delays thearrival of the signal Vs at the negative input terminal of thetransceiver 203. (Note: Vs generally refers to the peak voltage of thevoltage source, as opposed to the peak to peak voltage.) Thus, thesignal Vs will arrive at the positive terminal of the transceiver 203 attime T1 before the signal Vs arrives at the negative terminal of thereceiver. If the delay 25 causes a delay of time T1 that issubstantially equal to one half of the period of a carrier signalmodulated by the data signal, the transceiver 203 will see a voltagedifference between its positive and negative terminals, and deliver anoutput voltage, that approximates twice Vs. Alternately, if the delay 25causes a delay of time T1 that is substantially equal to one quarter ofthe period of the carrier signal modulated by the data signal, thetransceiver 90 will deliver an output voltage that approximates Vsmultiplied by the square root of two.

One method of causing a delay 25 along path C may be to increase thedistance that the signal must travel to reach the transceiver 203. Onemethod of purposely implementing such a delay is to construct path C tobe longer than path B by a distance equal to the portion of thewavelength for which a delay is desired. Thus, data from a single commonsource location may be transmitted and traverse two data paths on routeto a common receiving location. A delay may be added to one path with areceiving device differentially receiving the signal from the two paths.If the delay for a given signal along one path is not ideal (e.g., ismuch less than the period), the differential voltage at the transceiverterminals may be smaller than Vs thereby resulting in an apparentcoupling loss. However, depending on numerous factors some coupling lossmay be tolerable or even desirable.

Referring to FIG. 5, the data signals (Vs) are transmitted along the MVpower line from the left, as indicated by the arrow Vs. As the datasignals Vs traverse the power line, different locations on the powerline may be at different voltage potentials due to the changing phase ofthe data signal. In this example embodiment, the energy of the datasignal will propagate down the power line toward point A. In thisexample, point A is a first connection point. At point A, a portion ofthe energy of the data signal will propagate along path Q and conductor253 to the positive terminal of an isolation transformer 235. Inaddition, a second portion of the energy of the data signal willcontinue propagating down the power line until reaching point B. In thisexample, point B is a second connection point to the power line 110. Atpoint B, a portion of the remaining energy of the data signal willpropagate along path P and conductor 255 to the negative terminal ofisolation transformer 235. Also, note that a third portion of the energyof the data signal may be reflected back by the real and presentimpedance discontinuity created by the junction at point B. Thisreflected power may contribute to both the insertion loss and throughloss of a coupler 237, because none of that power reaches thetransceiver 203, nor travels past the coupler 237.

As illustrated in FIG. 5, the data signals traversing along path P musttraverse a longer distance to reach the isolation transformer 235 thanthe data signals traveling along path A. In this example embodiment thepath distance between the isolation transformer 235 and point A mayequal the path distance between the isolation transformer 235 and pointB. Consequently, the additional distance that the data signals traversealong path P may substantially equal the distance d1 between connectionspoints A and B along the power line. Thus, in this embodiment, thecloser that the distance between points A and B approximates one-half awavelength of the carrier signal used to communicate the data signals,the closer the received signal will be to approximating twice Vs (i.e.,twice Vs that exists at connection point A). As will be evident to thoseskilled in the art, Vs at point A may be less than the voltagetransmitted from the transmitter due to the attenuation of the signalprior to it reaching point A.

The current from the data signals reaching the isolation transformer 235at the primary winding will induce a voltage (Vin) across the secondarywinding that corresponds to the data signal. Such corresponding signalmay then be received and processed by the transceiver 203. In thisembodiment, fuses 252 a, 252 b may be included to ensure safety ofpersonnel in the event a fault occurs.

For data signals originating at the transceiver 203, the data signalsare transmitted to the isolation transformer 235 resulting in adifferential voltage Vin on the primary winding. The voltage Vin isconducted to the power line at connection points A and B. A portion ofthe power of the data signals may be transmitted in both directions onthe power line away from the coupler 237. Specifically, when the datasignal from path P reaches point B, it will be travel in both directionsalong the MV power line. When a portion of that energy reaches point A,it will be added to the energy of the data signals that reach point A bytraveling along path Q. However, because the data signal that traversespath P was transmitted with substantially the same magnitude and withopposite polarity (differentially) and has traveled a greater distanceto reach point A, its energy will not “cancel out” the data signals frompath Q, but instead may increase the energy of the data signalstraveling upstream (e.g., to the left in the figure).

In this example embodiment the excess distance that the transmitted datasignal travels along path P to reach point A, in comparison to thedistance traveled along path Q to reach point A, may substantially equalthe distance d1 along the power line between points A and B.Accordingly, the more precisely that the distance between points A and B(or more exactly A+B+P−Q) approximates one-half the wavelength of thecarrier signal used to communicate the data signals, the closer thetransmitted signal (at point A) may approximate twice Vin (i.e., twiceVin transmitted by isolation transformer 235). In a system that usesmultiple carrier frequencies, the distance between points A and B mayapproximate one-half the wavelength of any of the carrier frequencies.As will be evident those skilled in the art, transmission and receptionof data signals to and from the other direction on the power line willoperate in substantially the same manner.

In some instances, depending on the frequencies used to communicate thedata signals, a half (or even quarter) of a wavelength may be too greata distance to make the coupler economically feasible or to permit apractical installation. In other embodiments, depending on variousfactors, including but not limited to the quantity of power line noise,the transceiver 203 sensitivity, and the power of the data signals, itmay be possible to make the distance between the connection points A andB less than one half or one quarter of a wavelength. In one exampleembodiment, the distance between the two connection point locations onthe MV power (points A and B) preferably may be greater than fivepercent (5%), more preferably greater than seven and a half percent(7.5%), even more preferably greater than ten percent (10%), and stillmore preferably greater than twenty percent (20%) of the wavelength of acarrier frequency or of the lowest carrier frequency used to communicatethe data signals. As is known to those skilled in the art, thewavelength is equal to the speed of propagation of the wave (which mayapproximate the speed of light) divided by its frequency. Thus, for datasignals transmitted using carrier signals in the 30-50 Mhz band, thedistance between the two connection points may preferably be greaterthan five percent (5%), more preferably greater than seven and a halfpercent (7.5%), even more preferably greater than ten percent (10%), andstill more preferably greater than twenty percent (20%) of thewavelength of the 30 Mhz carrier signal (i.e., the lowest carrierfrequency). Because the 30 Mhz carrier signal has a wavelength of lessthan 394 inches on the MV wire, the distance between the two connectionpoints may preferably be greater than 19.6 inches (5%), more preferablygreater than 29.4 inches (7.5%), even more preferably greater than 39.2inches (10%), and still more preferably greater than 78.4 inches (20%).It will be recognized to those skilled in the art that if the frequencyband of carriers is very wide, in comparison to the lowest carrierfrequency, it may be desirable to set the distance between theconnection points to be a quarter of a wavelength of a carrier near themiddle of the frequency band.

FIG. 6 shows a portion 260 of a PLCS in which a power line communicationdevice (PLCD) 202 is coupled to a single MV phase conductor 110 via thecoupling device, according to another example embodiment of the presentinvention. This embodiment of the coupling device may include the samecomponents as the coupling device of FIG. 3 a. In particular, thecoupling device may include a balun 234, a pair of lightening arrestors216, and a pair of air core inductors 214 a,b (or other high frequencyimpedance devices).

In the embodiment of FIG. 6, a first air core inductor 214 a may becoupled to a first lightening arrestor 216 a (via a conductor 226 a)between the energized conductor 110 and the neutral conductor 210.Similarly, a second air core inductor 214 b may be coupled to a secondlightening arrestor 216 b (via conductor 226 b) the energized conductor110 and the neutral conductor 210. The balun 234 has a first winding 238and a second winding 236. One end of the first winding 238 may becoupled to node 219 a to which is connected to both the first air coreinductor 214 a and the first lightening arrestor's 216 a. Similarly, thesecond end of the first winding 238 may be coupled to node 219 b towhich is connected both the second air core inductor 214 b and thesecond lightening arrestor's 216 b. In this embodiment, the air coreinductors 214 a and 214 b are connected to the neutral conductor ontheir second ends via separate conductors. This embodiment also includesthe two wire transmission line formed by conductors 226. Alternately,the two air core inductors 214 could be connected to the neutralconductor 21 via a common conductor as illustrated in FIG. 3 b. In suchan alternate embodiment, the air core inductors 214 may be physicallypositioned adjacent the lightening arrestors 216 a,b so that theconductors 226 may not be present or, if present, may not form a twopair transmission line.

The air core inductors 214 that form the high frequency impedancesdescribed above may be implemented in various embodiments. For example,in one embodiment, the air core inductors comprise an air core coil inthe shape of a spiral that is formed of copper wire. Each loop of thespiral conductor may be insulated from other loops by a dielectric. Thecopper wire may have a rectangular cross section to thereby decrease theoverall size of the inductor for a given inductance and DC currenthandling capability. The high frequency impedances of other embodimentsof the coupler may be formed with other types of inductors and/or otherlow pass filters such as, for example, a copper wire that is looped oneor more times through the center of a magnetically permeable toroid(e.g., a ferrite toroid).

FIG. 7 illustrates an example implementation of a single phase couplersimilar to the embodiment shown in FIG. 2. In this embodiment, the aircore inductor 214 and the balun 212 are housed inside a housing that isattached to a bracket assembly. In addition, the lightening arrestor 216is also attached to the bracket assembly so that mounting of the bracketassembly provides the physical installation of the components of thecoupler. In a multiphase coupler, two air core inductors 214 may bedisposed in the housing and two arrestors may be attached to the bracketassembly. For example, FIG. 8 illustrates the configuration of two aircore inductors 214 a,b that are to be mounted inside such a housing. Asillustrated, the two air core inductors 214 of this embodiment areformed of a copper conductor having spiral configuration. The first ends(214 c and 214 d) of each air core inductor 214 a,b are connected to thebalun 234 and also connected to the second ends of the lighteningarrestors (not shown) via bolt that extends through the housing and isexposed on the opposite site of the housing. The second ends of the aircore conductors are connected together and also connected to connector317 a, which is to be connected to conductor 317 (shown in FIG. 3 b),which connects to the neutral conductor 210. Other implementations andconfigurations for mounting the coupler and housing the components arewithin the scope of the present invention.

Communication Links and Communication Nodes

The power line communication system 104 (see FIG. 1) may includecommunication links formed between communication nodes 128 over acommunication medium. Some links may be formed over the MV power lines110. Some links may be formed over LV power lines 114. Other links maybe gigabit-Ethernet links 152, 154 formed, for example, using a fiberoptic cable. Thus, some links may be formed using a portion 101 of thepower system infrastructure, while other links may be formed overanother communication media, (e.g., a coaxial cable, a T-1 line, a fiberoptic cable, wirelessly (e.g., IEEE 802.11a/b/g, 802.16, 1G, 2G, 3G, orsatellite such as WildBlue®)). The links formed by wired or wirelessmedia may occur at any point along a communication path between abackhaul node 132 and a user device 130.

Each communication node 128 may be formed by one or more communicationdevices. Communication nodes which communicate over a power line mediuminclude a power line communication device (PLCD). Exemplary PLCD includea backhaul device 138, an access device 139, and a repeater.Communication nodes which communicate wirelessly may include a mobiletelephone cell site or a wireless access point having at least awireless transceiver. Communication nodes which communicate over acoaxial cable may include a cable modem. Communication nodes whichcommunicate over a twisted pair wire may include a DSL modem or othermodem. A given communication node typically will communicate in twodirections (either full duplex or half duplex), which may be over thesame or different types of communication media. Accordingly, acommunication node 128 may include one, two or more communicationdevices.

A backhaul node 132 may serve as an interface between a power lineportion (e.g., an MV power line 110) of the system 104 and an upstreamnode, which may be, for example, an aggregation point 124 that mayprovide a connection to an IP network 126. The backhaul node 132 maycommunicate with its upstream device via any of several alternativecommunication media, such as a fiber optic (digital or analog (e.g.,Wave Division Multiplexed), coaxial cable, WiMAX, IEEE, 802.11, twistedpair and/or another wired or wireless media. Downstream communicationsfrom the IP network 126 typically are communicated through theaggregation point 124 to the backhaul node 132. The aggregation point124 typically includes an Internet Protocol (IP) network data packetrouter and is connected to an IP network backbone, thereby providingaccess to an IP network 126 (i.e., can be connected to or form part of apoint of presence or POP). Any available mechanism may be used to linkthe aggregation point 124 to the POP or other device (e.g., fiber opticconductors, T-carrier, Synchronous Optical Network (SONET), and wirelesstechniques). Thus, a backhaul node may include a first modem forcommunicating over a fiber optic conductor, a second modem forcommunicating over an MV power line, a third modem for communicatingwith one or more user devices such as over a low voltage power line orwirelessly. In addition, a backhaul node may include a processor and arouting device (e.g., router, bridge, switch, etc.) to control thedestination of received data packets.

An access node 134 may serve one or more user devices 130 or othernetwork destinations. Upstream data may be sent, for example, from auser device 130 to an access node 134. Other data also, such as powerline parameter data (e.g., from parameter sensing devices) may bereceived by an access node's power line communication device 139. Thedata enters the network 104 along a communication medium coupled to anaccess node 134. The data is routed through the network 104 to abackhaul node 132, (or a local destination, such as another user device130). Downstream data is sent through the network 104 to a user device130. Thus, an access node may include a first for communicating over anMV power line (via a coupler), a second modem for communicating with oneor more user devices such as over a low voltage power line orwirelessly. In addition, an access node may include a processor and arouting device (e.g., router, bridge, switch, etc.) to control thedestination of received data packets.

Exemplary user devices 130 include a computer 130 a, LAN, a WLAN, router130 b, Voice-over IP endpoint, game system, personal digital assistant(PDA), mobile telephone, digital cable box, power meter, gas meter,water meter, security system, alarm system (e.g., fire, smoke, carbondioxide, security/burglar, etc.), stereo system, television, fax machine130 c, HomePlug residential network, or other device having a datainterface. A user device 130 may include or be coupled to a modem tocommunicate with a given access node 134. Exemplary modems include apower line modem 136, a wireless modem 131, a cable modem, a DSL modemor other suitable transceiver device.

A repeater node 135 may receive and re-transmit data (i.e., repeat), forexample, to extend the communications range of other communicationelements. As a communication traverses the communication network 104,backhaul nodes 132 and access nodes 134 also may serve as repeater nodes135, (e.g., for other access nodes and other backhaul nodes 132).Repeaters may also be stand-alone devices without additionalfunctionality. Repeaters 135 may be coupled to and repeat data on MVpower lines or LV power lines (and, for the latter, be coupled to theinternal or external LV power lines).

Communication nodes which access a link over a wireless medium mayinclude a wireless access point having at least a wireless transceiveror a mobile telephone cell site (e.g., a micro or pico cell site).Communication nodes which access a link over a coaxial cable may includea cable modem. Communication nodes which access a link over a T-1 wiremay include a DSL modem. According to an embodiment of a power linecommunication device, a backhaul device 138 or access device 139 orrepeater may establish links over MV power lines 110, LV power lines114, wired media, and wireless media. Accordingly, a given communicationnode may communicate along two or more directions establishing multiplecommunication links, which may be formed along the same or differenttypes of communication media.

The communication nodes with which the coupling devices of the presentinvention are used may be configured to determine when a lighteningarrestor 216 that is forming part of the coupling device has been blown,which, for example, may be caused by a lightening strike. For example,if communications with a particular PLCD are no longer possible fromother PLCDs, the arrestor 216 may be faulted. Different arrestors mayfault differently. Consequently, communications may remain possible withsome other arrestors even after the arrestor is blown due to alightening strike. In such causes, the electrical characteristics (e.g.,the capacitance and/or resistance) of the faulted lightening arrestormay be different from the characteristics of the arrestor before it wasblown. The change in the characteristics may cause a change in thetransfer function of the arrestor for frequencies of communications,which in turn may cause an increase in insertion loss and a reductionbandwidth. Detection of a blown lightening arrestor by a PLCD may resultin transmission of a notification by the PLCD to its upstream device,through the internet, to a remote computer system, which storesinformation of the location (e.g., pole number) of the blown arrestor inorder to dispatch crews to replace the arrestor.

The couplers of the present invention may also be used with existingarrestors that are already installed. For example, one process maycomprise identifying installed arrestors and installing the air coreinductor, balun, and PLCD.

Network Communication Protocols:

The communication network 104 may provide high speed internet access andother high data-rate data services to user devices, homes, buildings andother structure, and to each room, office, apartment, or other unit orsub-unit of multi-unit structure. In doing so, a communication link isformed between two communication nodes 128 over a communication medium.Some links are formed by using a portion 101 of the power systeminfrastructure. Specifically, some links are formed over MV power lines110, and other links are formed over LV power lines 114. Still otherlinks may be formed over another communication media, (e.g., a coaxialcable, a T-1 line, a fiber optic cable, wirelessly (e.g., IEEE802.11a/b/g, 802.16, 1G, 2G, 3G, or satellite such as WildBlue®)). Somelinks may comprise wired Ethernet, multipoint microwave distributionsystem (MMDS) standards, DOCSIS (Data Over Cable System InterfaceSpecification) signal standards or another suitable communicationmethod. The wireless links may also use any suitable frequency band. Inone example, frequency bands are used that are selected from amongranges of licensed frequency bands (e.g., 6 GHz, 11 GHz, 18 GHz, 23 GHz,24 GHz, 28 GHz, or 38 GHz band) and unlicensed frequency bands (e.g.,900 MHz, 2.4 GHz, 5.8 GHz, 24 GHz, 38 GHz, or 60 GHz (i.e., 57-64 GHz)).

Accordingly, the communication network 104 includes links that may beformed by power lines, non-power line wired media, and wireless media.The links may occur at any point along a communication path between abackhaul node 132 and a user device 130, or between a backhaul node 132and a distribution point 127 or aggregation point 124.

Communication among nodes 128 may occur using a variety of protocols andmedia. In one example, the nodes 128 may use time division multiplexingand implement one or more layers of the 7 layer open systemsinterconnection (OSI) model. For example, at the layer 3 ‘network’level, the devices and software may implement switching and routingtechnologies, and create logical paths, known as virtual circuits, fortransmitting data from node to node. Similarly, error handling,congestion control and packet sequencing can be performed at Layer 3. Inone example embodiment, Layer 2 ‘data link’ activities include encodingand decoding data packets and handling errors of the ‘physical’ layer 1,along with flow control and frame synchronization. The configuration ofthe various communication nodes may vary. For example, the nodes coupledto power lines may include a modem that is substantially compatible withthe HomePlug 1.0 or A/V standard. In various embodiments, thecommunications among nodes may be time division multiple access orfrequency division multiple access.

Examples of access devices 139, backhaul points 138, repeaters 158,power line servers, and other components are provided in U.S. Pat. No.7,224,272, issued May 29, 2007, entitled “Power Line Repeater System andMethod,” which is hereby incorporated by reference in its entirety. Adetailed description of other such devices is provided in U.S. patentapplication Ser. No. 11/423,206 filed Jun. 9, 2006, entitled “Power LineCommunication Device and Method,” which is hereby incorporated byreference in its entirety.

It is to be understood that the foregoing illustrative embodiments havebeen provided merely for the purpose of explanation and are in no way tobe construed as limiting of the invention. Words used herein are wordsof description and illustration, rather than words of limitation. Inaddition, the advantages and objectives described herein may not berealized by each and every embodiment practicing the present invention.Further, although the invention has been described herein with referenceto particular structure, materials and/or embodiments, the invention isnot intended to be limited to the particulars disclosed herein. Rather,the invention extends to all functionally equivalent structures, methodsand uses, such as are within the scope of the appended claims. Thoseskilled in the art, having the benefit of the teachings of thisspecification, may affect numerous modifications thereto and changes maybe made without departing from the scope and spirit of the invention.

1. A power line coupler configured to couple communication signalsbetween a communication device having a first terminal and a secondterminal and a power distribution system having a first and a secondoverhead energized power line conductor, and a neutral conductor,comprising: a first capacitor having a first end and a second end;wherein said first end of said first capacitor is connected to the firstpower line conductor; a second capacitor having a first end and a secondend; wherein said first end of said second capacitor is connected to thesecond power line conductor; a transformer forming at least part of abalun and having a first winding and a second winding; wherein saidfirst winding has a first end coupled to the first terminal of thecommunication device; wherein said first winding has a second endcoupled to the second terminal of the communication device; wherein saidsecond winding has a first end coupled to said second end of said firstcapacitor; and wherein said second winding has a second end coupled tosaid second end of said second capacitor.
 2. The coupler of claim 1,further comprising: a first high frequency impedance having a first endconnected to said second end of said first capacitor, said first highfrequency impedance having a second end connected to the neutralconductor; a second high frequency impedance having a first endconnected to said second end of said second capacitor, said second highfrequency impedance having a second end connected to the neutralconductor.
 3. The coupler of claim 2, wherein said second end of saidfirst impedance and said second end of said second impedance areconnected to the neutral conductor via a common conductor.
 4. Thecoupler of claim 3, wherein said first capacitor comprises a firstlightening arrestor and said second capacitor comprises a secondlightening arrestor.
 5. The coupler of claim 2, wherein said first highfrequency impedance and said second high frequency impedance eachcomprise an air core inductor.
 6. The coupler of claim 5, wherein saidfirst capacitor comprises a first lightening arrestor and said secondcapacitor comprises a second lightening arrestor.
 7. The coupler ofclaim 2, wherein said first high frequency impedance and said secondhigh frequency impedance each comprises a spiral conductor.
 8. Thecoupler of claim 2, wherein said first capacitor comprises a firstlightening arrestor and said second capacitor comprises a secondlightening arrestor.
 9. The coupler of claim 2, wherein: said first endof said first high frequency impedance is connected to said second endof said second capacitor via a first conductor; said first end of saidsecond high frequency impedance is connected to said second end of saidsecond capacitor via a second conductor; and said first conductor andsaid second conductor form a two wire transmission line.
 10. The couplerof claim 1, wherein said first capacitor comprises a first lighteningarrestor and said second capacitor comprises a second lighteningarrestor.
 11. A power line coupler configured to couple communicationsignals to and from a power distribution system having a first and asecond overhead energized power line conductor, and a neutral conductor,comprising: a first lightening arrestor having a first end and a secondend, wherein said first end of said first lightening arrestor isconnected to the first power line conductor; a first high frequencyimpedance having a first end connected to said second end of said firstlightening arrestor, said first impedance having a second end connectedto the neutral conductor; a second lightening arrestor having a firstend and a second end, wherein said first end of said second lighteningarrestor is connected to the second power line conductor; a second highfrequency impedance having a first end connected to said second end ofsaid second lightening arrestor, said second impedance having a secondend connected to the neutral conductor; a transformer forming at leastpart of a balun and having a first winding and a second winding; whereinsaid first winding is coupled to a communication device; wherein saidsecond winding has a first end connected to said first end of said firsthigh frequency impedance; and wherein said second winding has a secondend connected to said first end of said second high frequency impedance.12. The coupler of claim 11, wherein said first high frequency impedanceand said second high frequency impedance each comprises an air coreinductor.
 13. The coupler of claim 11, wherein said first and secondlightening arrestors are configured to differentially couplecommunications signals to the first and second power line conductors.14. The coupler of claim 13, wherein the communication device isconfigured to: determine that the first lightening arrestor is blown;and transmit a notification upon determining that the first lighteningarrestor is blown.
 15. The coupler of claim 11, wherein: said first endof said first impedance is connected to said second end of said firstlightening arrestor via a first conductor; said first end of said secondimpedance is connected to said second end of said second lighteningarrestor via a second conductor; and said first conductor and saidsecond conductor are configured to form a two wire transmission line.16. The coupler of claim 11, wherein said first high frequency impedanceand said second high frequency impedance each comprises an air coreinductor having a spiral portion.
 17. The coupler of claim 11, whereinsaid first high frequency impedance and said second high frequencyimpedance are connected to the neutral conductor via a common conductor.18. A method of coupling communication signals to and from first andsecond energized power line conductors, comprising: providing a firstdata path from the first energized conductor through a first lighteningarrestor to a first terminal of a communication device; wherein thefirst data path includes a balun disposed between the first lighteningarrestor and the first terminal of the communication device; providing asecond data path from the second energized conductor through a secondlightening arrestor to a second terminal of the communication device;and wherein the second data path includes the balun which is furtherdisposed between the second lightening arrestor and the second terminalof the communication device.
 19. The method of claim 18, furthercomprising: providing a first lightening path configured to conductelectricity from a lightening strike that includes the first lighteningarrestor and a ground conductor; and providing a second lightening pathconfigured to conduct electricity from a lightening strike that includesthe second lightening arrestor and the ground conductor.
 20. The methodof claim 19, wherein the first lightening path and the second lighteningpath further include a common conductor.
 21. The method of claim 19,wherein: the first lightening path further includes a first highfrequency impedance; and the second lightening path further includes asecond high frequency impedance.
 22. The method of claim 19, wherein:the first lightening path further includes a first air core inductor;and the second lightening path further includes a second air coreinductor.
 23. The method of claim 22, wherein the first air coreinductor and the second air core inductor each comprises a spiralportion.
 24. The method of claim 18, further comprising differentiallycoupling a communication signal from the communication device to thefirst and second energized power line conductors via the first data pathand the second data path.
 25. The method claim 18, further comprising:providing a first conductive path that includes a first high frequencyimpedance between the first lightening arrestor and a neutral conductor;and providing a second conductive path that includes a second highfrequency impedance between the second lightening arrestor and theneutral conductor.
 26. The method claim 18, further comprising:providing a first conductive path that includes a first air coreinductor between the first lightening arrestor and a neutral conductor;and providing a second conductive path that includes a second air coreinductor between the second lightening arrestor and the neutralconductor.